This invention relates to a method for producing a steering wheel on which a transfer ink is printed, by bringing the steering wheel into contact with a transfer ink-coated film floated and advanced on a water-surface.
Conventionally, a pattern such as wood grain pattern has been printed onto a rim section of a steering wheel by utilizing a technique of a liquid pressure transfer print. For example, Japanese Patent Laid-Open Publication No. 61-5981 discloses a conventional technique of a liquid pressure transfer print for the rim section of the steering wheel. In this conventional technique, as shown in FIG. 6, the steering wheel 1A' is set upright so that its rim section 4' is brought into contact with a transfer film F', while the steering wheel 1A' is rotated and delivered in the traverse direction for printing a wood grain pattern on the whole surface around the rim section 4'. By doing so, this conventional technique has an effect that the rim section 4' looks like as if it were manufactured by forming a round wood rod.
In such a conventional technique of a liquid pressure transfer print, a joint line of the transfer pattern is located at the most inner portion of the steering wheel, resulting in the joint line being clearly visible from the driver-side. In a conventional method related to a liquid pressure transfer print for the rim section of the steering wheel, manufactures were likely to think that the joint line of the transfer pattern was not so serious problem, because, they judged the design of the rim section only by whether, onto the surface of the rim section, the pattern of a wood grain, e.g., cross grain or straight grain of wood, was printed or not.
However, in these days, a front panel and side panels often have grain patterns of precious wood, hence, also in the case of a steering wheel, not a grain pattern of common wood but a grain pattern of precious wood is desired. That is to say, high level design is required in the steering wheel, thus, the above mentioned joint line of the transfer pattern becomes an important matter.
Therefore, instead of the conventional method of a liquid pressure transfer print disclosed in, for example, the above Japanese Patent Laid-Open Publication No. 61-5981, the inventors tried a method for attaining a steering wheel with a joint line of a transfer pattern located at the back-side of the wheel so as not to be visible from the driver-side. In the method tried by the inventors, as shown in FIG. 7, a steering wheel 1A' was immersed straight in a transfer liquid at a predetermined transfer angle formed when the steering wheel 1A' is pressed onto a transfer film F'. In this trial, was found a specific problem accompanied with the liquid pressure transfer print for the steering wheel 1A'. More particularly, in a steering wheel 1A', it is difficult to apply uniformly a liquid pressure transfer print of e.g., a wood grain pattern to the whole surface around an annular rim section 4' provided with spokes 3' extending from its inner side, resulting in pattern-missing and pattern-distortion occurring.
The pattern-missing means a situation where a large area of the pattern is missing at a space requiring a transfer print. In the steering wheel, when the part of the rim section or spoke is immersed in the transfer liquid while it is brought into contact with the transfer film, this film might be used up and removed. Accordingly, after that, when the other part of the rim section is immersed in the transfer liquid, there is no transfer film, resulting in pattern-missing occurring.
The pattern-distortion occurs in the following manner. When a transfer film is immersed partly in a transfer liquid together with an object to be printed, the immersed part of the film pulls another part of the film remained on the liquid-surface. In parts of the object which are simultaneously immersed together with the film, the resultant pattern does not deform, since tension is not caused there, although tension is caused on the following part of the transfer film remained on the liquid-surface. A steering wheel has, at the preceding-side and trailing-side in its delivering direction, two quarter-arc portions each of which is immersed simultaneously in the transfer liquid. Also, the steering wheel has, at the right-side and left-side of its delivering direction, two quarter-arc portions each of which is immersed gradually with a time lag. Among these quarter-arc portions, the pattern-distortion occurs in the above right and left portions each of which is immersed gradually with a time lag.
Therefore, a solution has been considered for eliminating or minimizing such pattern-missing and pattern-distortion. However, some kinds of steering wheels have parts requiring no liquid pressure transfer print. For example, grip parts covered with leather and spoke-connecting portions in a rim section are not to be printed. Thus, the inventors have supposed that even if the pattern-missing and pattern-distortion might occur in the grip parts and spoke-connecting portions, by utilizing this situation, a liquid pressure transfer print can be applied to only parts requiring good appearance, which results in a desired steering wheel.